respiration experiments

what is the practical?

• investigation into the effect of a named variable on the rate of respiration of cultures of single-celled organisms

background information?

• yeast is a single-celled organism that respires both aerobically and anaerobically

• during respiration, electrons are transferred to synthesise ATP

• respiration can be measured using a redox indicator dye such as methylene blue

• this accepts these electrons and undergoes a colour change from blue to colourless

equipment list?

• yeast and glucose in a buffered solution

• water bath

• thermometer

• test tubes

• timer

method?

in this method, the named variable is temperature

• set up a water bath at 35C

• add 5cm³ of yeast and glucose solution to 3 test tubes. place the test tubes in the water bath and leave them, for the solution to equilibrate for 10mins

• add 2cm³ of methylene blue to the test tubes and start the timer. shake for 10seconds and place test tubes back into the water bath

• record how long it takes for the methylene blue to turn colourless for each test tube

• repeat the experiment using temperature of 40C, 50C, 60C, and 70C

• find the mean of the results for each temperature and use to calculate the average rate of respiration

*rate of respiration = 1/ mean time

• plot a graph of rate of respiration against temperature

conclusion?

• yeast has an optimum temperature range for respiration, which is shown by the peak on the graph

• as the temperature moves away from the optimum, the rate of reaction will decrease as enzyme action decreases, and at high temperatures denaturation may occur

• as enzymes are crucial to respiration, as their activity decreases, so does the rate of respiration.

• this means that the methylene blue will take longer to turn colourless when the temperature is further from the optimum